Writing and Reading Non-openPMD Infos

[ax3l]

It would be necessary to allow storing non-openPMD information as well.

In the simple case, this means adding additional, user-defined attributes to records, record-components and paths.

In the more complex case, application specific states such as RNG states, unqiue-number-generator states, etc. need to be stored as records outside of the openPMD-interpreted paths.

[anokfireball]

The simple case is already possible, maybe not made explicit enough yet. Every "position" in an openPMD hierearchy (which in this APIs terms is an Attributable) supports a templated operation setAttribute, taking a string and a generic argument whose type has to map to a supported Datatype

Here's an example demonstrating said feature by annotating the root group with a std::string.

[ax3l]

That's already a great start, thx! :)

The latter case is quite relevant for PIConGPU checkpoints.

[ax3l]

cc @ejcjason you also need this, right?

[JunCEEE]

cc @ejcjason you also need this, right?

I cannot access the link "here", but I guess the suggested solution is to change the attribute of "position" under one particle group into something we want. That's good. But what if we want to add one group, say "observable", in the iteration group (i.e., in the same level of particles)?

• data/
  • 1/
    • observable/
    • particles/
      • Cu

It seems that the above solution doesn't work in this case, because there is no command like i.meshes[xx] or i.particles[xx] to create the observable. Maybe it can be achieved if we have something to change the group name of particles or meshes?

[ax3l]

Links updated with permanently accessible examples. setAttribute examples is now also in the manual.

Yes, what you want is to side-channel to the low-level write API to write groups and datasets outside of openPMD. That's also what I meant.

Maybe it can be achieved if we have something to change the group name of particles or meshes?

Or are you already good if you can change the meshesPath and particlesPath that we pick before we write? Probably not really.

[pgrete]

What the current status of supporting reading/writing other group data, @ax3l ?
I didn't find any more recent and we have a use case to store data that is not tied to a mesh (or particle).